1. Field of the Invention
The present invention relates to a mask inspecting apparatus, and more particularly to a mask inspecting apparatus for use in an electron beam exposure apparatus, which transfers a mask pattern of a stencil mask (a mask with apertures) onto a resist layer on a semiconductor wafer in an equal size using an electron beam.
2. Description of the Related Art
Japanese Patent Application Publication No. 2001-227932 discloses a conventional mask inspecting apparatus, in which a mask is irradiated with a converged electron beam, the electron beam transmitting through the mask is then converted into light on a fluorescent plate, and an optical image resulting from this photo-conversion is converted into image signals with a CCD camera. The mask is then shifted in the X direction and the Y direction so that the whole surface of the mask is scanned with the electron beam, and the image signals picked up by the CCD camera are transferred in synchronism with this shifting of the mask to obtain an image of the whole mask surface.
However, since this conventional mask inspecting apparatus is a dedicated mask inspecting apparatus, it has a problem that it cannot inspect a mask being used in the exposure apparatus.
On the other hand, U.S. Pat. No. 5,831,272 corresponding to Japanese Patent No. 2951947 discloses an electron beam proximity exposure apparatus as an exposure apparatus using this kind of mask. In this electron beam proximity exposure apparatus, the mask is arranged in proximity to the wafer (e.g., with an interval of 50 xcexcm between the mask and the wafer), and the mask is irradiated with an electron beam coming vertically on it and scanned with the electron beam, so that the electron beam transmitting through the mask pattern of the mask can transfer the mask pattern of the mask on to the resist layer on the wafer in an equal size. In some cases, smear sticks to the back face of the mask arranged in proximity to the wafer, however, it is impossible to frequently inspect the mask with the conventional mask inspecting apparatus to detect the smear of the mask or any such trouble, since the mask has to be transferred for the inspection from the exposure apparatus to the inspecting apparatus.
The present invention, attempted in view of this circumstance, is intended to provide a mask inspecting apparatus capable of not only inspecting a mask with an electron beam used for proximity exposure utilizing the features of the electron beam proximity exposure apparatus but also obtaining an image of the mask pattern which is the same as the mask pattern actually transferred onto the wafer.
In order to attain the object stated above, the present invention is directed to a mask inspecting apparatus incorporated into an electron beam proximity exposure apparatus in which a mask is arranged in proximity to a wafer, and a mask pattern formed on the mask is transferred onto a resist layer on the wafer by scanning the mask with an electron beam, the mask inspecting apparatus comprising: an electron beam image-capturing device arranged on one of a wafer stage on which the wafer is to be mounted and an inspecting stage, the electron beam image-capturing device receiving electrons originating from the electron beam transmitting through the mask pattern of the mask so as to capture an image of the transmitting electron beam; and a stage drive device which shifts the one of the wafer stage and the inspecting stage so that the electrons are brought to incidence on the electron beam image-capturing device when the mask is inspected.
According to the present invention, by shifting the electron beam image-capturing device using the wafer stage or inspecting stage, the electron beam for use in proximity exposure can be used to examine the state of the electron beam transmitting through the mask (i.e. the state of the mask pattern of the mask).
The electron beam image-capturing device may comprise a scanning electron microscope which receives secondary electrons generated from an edge portion on a lower face of the mask pattern of the mask.
Alternatively, the electron beam image-capturing device may comprise: a fluorescent plate provided at substantially the same height as an upper face of the wafer to be mounted on the wafer stage; and a microscopic image-capturing device which magnifies and captures an image produced on the fluorescent plate. In this case, the same image as the mask pattern actually transferred onto the wafer can be obtained. Furthermore, by monitoring an image captured through the electron beam image-capturing device, it can be monitored whether or not the mask is satisfactory and the state of the mask pattern.
Preferably, the electron beam proximity exposure apparatus comprises a control device which controls an angle of incidence of the electron beam on the mask pattern to compensate any distortion of the mask according to the image captured through the electron beam image-capturing device. Thus, even if the mask is distorted, an undistorted mask pattern could be transferred by exposure onto the wafer by controlling the angle of incidence of the electron beam on the mask pattern. It would also be possible to obtain the same mask pattern as the mask pattern transferred by exposure on the wafer by the electron beam image-capturing device according to the position of scanning with the electron beam, therefore enabling the angle of incidence of the electron beam to be determined so as not to distort the mask pattern transferred by exposure onto the wafer on the basis of that image.
Preferably, the mask inspecting apparatus further comprises an image-capturing device which captures an image of the mask pattern on an upper face of the mask. This enables images representing the mask patterns on the upper and lower faces of the mask to be captured (the line width of the upper face of the mask and that of the lower face of the mask are not necessarily identical), or the mask to be three-dimensionally inspected. The image-capturing device for the mask pattern on the upper face of the wafer is not limited to the electron beam image-capturing device, but a microscopic image-capturing device having a visible light source or the like can as well be used for instance.